% 將大地經緯度轉化為地磁經緯度
% 磁極點取:經度72.2°W,緯度80.0°N(IGRF,2011)
% 輸入及輸出值為弧度制單位(rad)
% by chensd HHU 2016.01.02
% 磁極點經緯度
b=80.0*pi/180;
l=-72.2*pi/180;
% 以下公式基於劉長建,2011
sb=sin(Bg)*sin(b)+cos(Bg)*cos(b)*cos(Lg-l);
Bm=asin(sb);
sl=cos(Bg)*sin(Lg-l)/cos(Bm);
cl=(sin(b)*sb-sin(Bg))/(cos(b)*cos(Bm));
Lm=atan2(sl,cl);